Yellow Equipment

Yellow equipment oil covers the transmission, drive train, final drive and wet brake fluids used in earthmoving and construction machinery such as dozers, graders, loaders and articulated dump trucks.

The defining specification here is TO-4, which sets a controlled friction requirement for powershift transmissions, oil-immersed brakes and hydraulic systems on heavy plant. Unlike an engine oil, a TO-4 fluid has to deliver consistent clutch engagement and quiet, chatter-free wet brake operation, so friction performance is tested directly rather than inferred. Grades are chosen by component and ambient temperature: SAE 10W for hydraulics and cold conditions, SAE 30 as the general transmission and drive train grade, and SAE 50 for final drives and hotter operating duty.

Using an engine oil where a TO-4 fluid is specified is a common and expensive mistake on yellow equipment.